We have finished approximately 50% of the proposed work as of 1 April 1980. In the next year we will finish collecting data on 15 subjects that will complete our inactive control group (2 subjects) and those training at 5 degrees C, 18 degrees C, and 30 degrees C. As in the original proposal, this work will consist of total body water and blood volume determinations at 0, 3, and 6 weeks of training (inactivity for controls), weekly VO2 max, and responses of all subjects to a standard work test both in the cool (5 degrees C) and warm (30 degrees C) climates. Blood samples will be obtained as will pertinent metabolic data.